Redox flow batteries are known as a type of high-capacity storage battery. A redox flow battery generally has an ion exchange membrane that separates an electrolyte solution, and electrode materials provided on both sides of the ion exchange membrane. The battery can be charged and discharged by making an oxidation reaction and a reduction reaction progress simultaneously on the electrode materials. Additionally, carbonaceous members are widely used as such electrode materials.
The supply of the electrolyte solution to the carbonaceous members is generally performed by using a pump or the like. If there is a pressure drop when passing liquid inside a redox flow battery, the overall energy efficiency of the battery decreases. For this reason, in Patent Document 1, it is described that the pressure drop can be reduced by forming grooves in the electrode materials. Additionally, Patent Document 2 describes that the pressure drop can be reduced by controlling the direction of flow of the electrolyte solution with respect to the carbonaceous members in a redox flow battery.
Various studies have also been performed on carbonaceous members for the purpose of improving battery performance. For example, in Patent Document 1 and Patent Document 2, carbon fleece and felt (non-woven fabrics) containing widely and commonly used carbon fibers (PAN-based carbon fibers) are used as the carbonaceous members. Patent Document 3 describes the use of vapor-grown carbon fibers in the electrode materials of redox flow batteries in order to improve the battery properties.